BRUSSELS (AP) — Belgian authorities are investigating whether three companies might have been involved in the illegal export to Syria of a chemical that could be used in the production of sarin gas.

Finance Minister Johan Van Overtveldt told The Associated Press the case against the companies is to come to court on May 15 for opening proceedings in the port city of Antwerp and centers on whether and how illegal products were exported between 2014 and 2016 despite the sanctions against the regime of President Bashar Assad.

Syria has been accused of several chemical attacks in the civil war, including some that used sarin gas.

The European Union has imposed ever-tighter sanctions on Assad, including on the export of several chemicals, since 2013. Knack magazine first reported that three interlinked Belgian companies — Danmar Logistics, AAE Chemie and the now-defunct Anex Customs — were able to continue exports of some chemicals until 2016. Among them was isopropanol, a chemical used in anything from paint to health products but that can also help produce sarin.

"It is indeed a shock to find out that there might be some link," Van Overtveldt said.

In line with an international agreement, Syria had destroyed its stocks of some 120 metric tons of isopropanol by May 2014. The Belgian court case will center on the possible export of 168 metric tons of isopropanol and tons more of three other products to Syria and Lebanon after that.

"The subpoena alleges that these firms have exported the chemical products without the proper license, without the export license," Antwerp court media judge Ronald Cassiers said.

Van Overtveldt said, though, that exports of isopropanol needed a special license only if it exceeded a density threshold, and it was up to the court to rule on that. "It is an important detail," he said.

He also insisted that the export of the product had been going on since 2010, when it was still legal, and had not started once Assad faced sanctions on chemicals. "They were destined at the time, and also later, for the painting industry."

An official at Danmar Logistics told the AP that he did not dispute that such products had been exported but insisted they had been checked and released by Belgian customs for exports.

The official spoke on condition of anonymity because of the ongoing investigation. "I don't know what they can hold against us," the official said.

The complaint before the Antwerp court was brought by the Belgian customs office.

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